Power conversion device

ABSTRACT

In a power conversion device, a main direct-current/direct-current (DC/DC) converter includes a first three-phase circuit capable of receiving and outputting a three-phase alternating current, a second three-phase circuit capable of receiving and outputting a three-phase alternating current, and an isolation transformer. A sub-DC/DC converter branches from the isolation transformer, and transforms a voltage of power supplied through the first three-phase circuit or the second three-phase circuit. The isolation transformer is provided between the first three-phase circuit and the second three-phase circuit, and transforms the voltage of the power supplied through the first three-phase circuit or the second three-phase circuit. The isolation transformer includes three coil units. The coil unit includes primary winding, main secondary winding, and sub secondary winding. The coil units are provided in the three phases, at least one for each phase.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to and incorporates by referencethe entire contents of Japanese Patent Application No. 2018-243839 filedin Japan on Dec. 27, 2018.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a power conversion device.

2. Description of the Related Art

Conventionally, for example, Japanese Patent No. 5577986 discloses anin-vehicle power supply device as a power conversion device. Thisin-vehicle power supply device is provided with a primary bridge circuitthat outputs alternating-current (AC) power, a transformer thattransforms the AC power output from the primary bridge circuit, asecondary bridge circuit that converts the AC power transformed by thetransformer into direct-current (DC) power, and a voltage regulatorcircuit on the secondary side that regulates a voltage of the AC powertransformed by the transformer. The transformer includes primary windingconnected to the primary bridge circuit, first secondary windingconnected to the secondary bridge circuit, and second secondary windingconnected to the voltage regulator circuit on the secondary side.

The in-vehicle power supply device described in JP 5577986 B mentionedabove supplies, for example, two kinds of power having differentvoltages, and thus, a ripple may occur in the power supplied to thevoltage regulator circuit on the secondary side through the secondsecondary winding. This problem leaves room for further improvements.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made in view of theabove-described circumstances, and an object thereof is to provide apower conversion device capable of appropriately supplying a pluralityof kinds of power having different voltages.

In order to solve the above mentioned problem and achieve the object, apower conversion device according to one aspect of the present inventionincludes a main DC/DC converter including a first three-phase circuitcapable of receiving and outputting a three-phase alternating current, asecond three-phase circuit capable of receiving and outputting athree-phase alternating current, and an isolation transformer providedbetween the first three-phase circuit and the second three-phasecircuit, and configured to transform a voltage of power supplied throughthe first three-phase circuit or the second three-phase circuit; and asub-DC/DC converter branching from the isolation transformer, andconfigured to transform the voltage of the power supplied through thefirst three-phase circuit or the second three-phase circuit, wherein theisolation transformer includes three coil units each having a primarywinding connected to one of phases of the first three-phase circuit, amain secondary winding electromagnetically coupled to the primarywinding, and connected to one of phases of the second three-phasecircuit, and a sub secondary winding electromagnetically coupled to theprimary winding or the main secondary winding, and connected to thesub-DC/DC converter, and the coil units are provided in the threephases, at least one for each phase.

According to another aspect of the present invention, in the powerconversion device, it is preferable that the power conversion deviceincludes an AC/DC circuit configured to output, to the main DC/DCconverter, a direct current power converted from an alternating currentpower supplied from an alternating current power supply; and a powerstorage unit configured to store the direct current power transformed bythe main DC/DC converter.

According to still another aspect of the present invention, in the powerconversion device, it is preferable that the power conversion deviceincludes a power storage unit configured to store a direct current powerand supply the direct current power to the main DC/DC converter; and aninverter circuit configured to output, to a load unit, an alternatingcurrent power converted from the direct current power transformed by themain DC/DC converter.

According to still another aspect of the present invention, in the powerconversion device, it is preferable that the power conversion deviceincludes a controller configured to control the inverter circuit and thesub-DC/DC converter, wherein the controller is configured to limitoutput power output from the inverter circuit to the load unit based ona maximum value of the output power and an output value of the sub-DC/DCconverter.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram illustrating a configuration example of apower conversion device according to an embodiment of the presentinvention;

FIG. 2 is a circuit diagram illustrating a charging example of the powerconversion device according to the embodiment;

FIG. 3 is a circuit diagram illustrating an alternating-current (AC)power supply example of the power conversion device according to theembodiment;

FIG. 4 is a flowchart illustrating a power limitation example during theAC power supply according to the embodiment;

FIG. 5 is a flowchart illustrating a power limitation example during theAC power supply according to a modification of the embodiment;

FIG. 6 is a circuit diagram illustrating an isolation transformer(No. 1) according to the modification of the embodiment; and

FIG. 7 is a circuit diagram illustrating an isolation transformer (No.2) according to the modification of the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following describes a mode (embodiment) for carrying out the presentinvention in detail with reference to the drawings. The presentinvention is not limited to the description of the embodiment to begiven below. Components to be described below include those easilyconceivable by those skilled in the art or those substantially identicalthereto. Moreover, configurations to be described below can be combinedas appropriate. Furthermore, the configurations can be variouslyomitted, replaced, or modified within the scope not deviating from thegist of the present invention.

EMBODIMENT

A power conversion device 1 according to the embodiment will bedescribed with reference to the drawings. FIG. 1 is a circuit diagramillustrating a configuration example of the power conversion device 1according to the embodiment. The power conversion device 1 is a devicethat is mounted on a vehicle and converts power. The power conversiondevice 1 is mounted on the vehicle, such as an electric vehicle (EV) ora plug-in hybrid vehicle (PHV), and charges a high-voltage battery 50and a low-voltage battery 70 with direct-current (DC) power convertedfrom alternating-current (AC) power supplied from an AC power supply 2(charging process). The power conversion device 1 supplies AC powerconverted from the DC power supplied from the high-voltage battery 50 toa load unit 3 (AC supply process).

As illustrated in FIG. 1, the power conversion device 1 is provided witha filter 10, a detector 20, a conversion circuit 30 serving as an AC/DCcircuit and an inverter circuit, a main DC/DC converter 40, thehigh-voltage battery 50 serving as a power storage unit, a sub-DC/DCconverter 60, the low-voltage battery 70, and a controller 80.

The filter 10 removes noise. The filter 10 is connected to the AC powersupply 2 (refer to FIG. 2), and removes noise from the AC power suppliedfrom the AC power supply 2 during the charging. The filter 10 isconnected to the conversion circuit 30 through a coil L7 d, and outputsthe AC power having got rid of the noise to the conversion circuit 30.The filter 10 removes noise from the AC power supplied from theconversion circuit 30 during the AC power supply. The filter 10 outputsthe AC power having got rid of the noise to the load unit 3.

The detector 20 detects currents and voltages. The detector 20 includescurrent sensors 21 a to 21 d and voltage sensors 22 a to 22 c. Thecurrent sensor 21 d is provided between the filter 10 and a switchingcircuit 31 of the conversion circuit 30, and detects a current flowingbetween the filter 10 and the switching circuit 31 of the conversioncircuit 30. The current sensor 21 d is connected to the controller 80,and outputs the detected current to the controller 80.

The current sensor 21 a is provided between the switching circuit 31 ofthe conversion circuit 30 and the main DC/DC converter 40. The currentsensor 21 a detects a current flowing between the switching circuit 31of the conversion circuit 30 and the main DC/DC converter 40. Thecurrent sensor 21 a is connected to the controller 80, and outputs thedetected current to the controller 80.

The voltage sensor 22 a is provided between the switching circuit 31 ofthe conversion circuit 30 and the main DC/DC converter 40. The voltagesensor 22 a detects a voltage applied between the switching circuit 31of the conversion circuit 30 and the main DC/DC converter 40. Thevoltage sensor 22 a is connected to the controller 80, and outputs thedetected voltage to the controller 80.

The current sensor 21 b is provided between a second three-phase circuit42 of the main DC/DC converter 40 and the high-voltage battery 50. Thecurrent sensor 21 b detects a current flowing between the secondthree-phase circuit 42 of the main DC/DC converter 40 and thehigh-voltage battery 50. The current sensor 21 b is connected to thecontroller 80, and outputs the detected current to the controller 80.

The voltage sensor 22 b is provided between the second three-phasecircuit 42 of the main DC/DC converter 40 and the high-voltage battery50. The voltage sensor 22 b detects a voltage applied between the secondthree-phase circuit 42 of the main DC/DC converter 40 and thehigh-voltage battery 50. The voltage sensor 22 b is connected to thecontroller 80, and outputs the detected voltage to the controller 80.

The current sensor 21 c is provided between a step-down circuit 62 ofthe sub-DC/DC converter 60 and the low-voltage battery 70. The currentsensor 21 c detects a current flowing between the step-down circuit 62of the sub-DC/DC converter 60 and the low-voltage battery 70. Thecurrent sensor 21 c is connected to the controller 80, and outputs thedetected current to the controller 80.

The voltage sensor 22 c is provided between the step-down circuit 62 ofthe sub-DC/DC converter 60 and the low-voltage battery 70. The voltagesensor 22 c detects a voltage applied between the step-down circuit 62of the sub-DC/DC converter 60 and the low-voltage battery 70. Thevoltage sensor 22 c is connected to the controller 80, and outputs thedetected voltage to the controller 80. As described above, the powerconversion device 1 is provided with the current sensors 21 a to 21 dand the voltage sensors 22 a to 22 c, and thereby can control thecurrent values, the voltage values, and power values withinpredetermined ranges, thus being capable of operating over a broad powerrange.

The conversion circuit 30 serves as the AC/DC circuit (power factorcorrection (PFC) circuit) during the charging, and serves as theinverter circuit during the AC power supply. In other words, the sameconversion circuit 30 is used both as the AC/DC circuit and the invertercircuit. The conversion circuit 30 includes the switching circuit 31 anda capacitor C1 a. The switching circuit 31 includes field-effecttransistors (FETs) Q1 a to Q4 a. In the switching circuit 31, the FET Q1a and the FET Q2 a are connected in series to form a first seriescircuit, and the FET Q3 a and the FET Q4 a are connected in series toform a second series circuit. In the switching circuit 31, the firstseries circuit is provided on the filter 10 side; the second seriescircuit is provided on the main DC/DC converter 40 side; and the firstand second series circuits are connected in parallel. In the switchingcircuit 31, a terminal on one side of the filter 10 is connected to aline between the FET Q1 a and the FET Q2 a, and a terminal on anotherside of the filter 10 is connected to a line between the FET Q3 a andthe FET Q4 a.

The switching circuit 31 is connected to the controller 80, and thecontroller 80 controls the FETs Q1 a to Q4 a. During the charging, theswitching circuit 31 converts the AC power supplied through the filter10 into DC power, and outputs the DC power to the main DC/DC converter40. In contrast, during the AC power supply, the switching circuit 31converts DC power output from the main DC/DC converter 40 into AC power,and outputs the AC power to the filter 10.

The capacitor C1 a smoothes the DC power. The capacitor C1 a isconnected in parallel to the switching circuit 31, and smoothes DC poweroutput from the switching circuit 31 during the charging. The capacitorC1 a also smoothes the DC power supplied to the switching circuit 31during the AC power supply.

The main DC/DC converter 40 converts the voltage of the DC power. Themain DC/DC converter 40 includes a first three-phase circuit 41, thesecond three-phase circuit 42, an isolation transformer 43, resonancecapacitors C1 b to C6 b, and resonance coils L1 d to L6 d.

The first three-phase circuit 41 is a half-bridge circuit capable ofreceiving and outputting a three-phase alternating current. The term“three-phase alternating current” refers to a combination of threealternating currents having current or voltage phases offset from oneanother by 120 degrees. The first three-phase circuit 41 includes FETsQ1 b to Q6 b. In the first three-phase circuit 41, the FET Q1 b and theFET Q2 b are connected in series to form a first series circuit; the FETQ3 b and the FET Q4 b are connected in series to form a second seriescircuit; and the FET Q5 b and the FET Q6 b are connected in series toform a third series circuit. In the first three-phase circuit 41, thefirst series circuit is provided on the conversion circuit 30 side; thethird series circuit is provided on the isolation transformer 43 side;the second series circuit is provided between the first series circuitand the third series circuit; and the first, second, and third seriescircuits are connected in parallel.

The first three-phase circuit 41 is connected to the conversion circuit30, the isolation transformer 43, and the controller 80. The controller80 controls the FETs Q1 b to Q6 b of the first three-phase circuit 41between on and off. During the charging, the first three-phase circuit41 converts the DC power supplied through the conversion circuit 30 intoAC power, and outputs the AC power to the isolation transformer 43. Incontrast, during the AC power supply, the first three-phase circuit 41converts AC power output from the isolation transformer 43 into DCpower, and outputs the DC power to the conversion circuit 30.

The second three-phase circuit 42 is a half-bridge circuit capable ofreceiving and outputting a three-phase alternating current. The secondthree-phase circuit 42 includes FETs Q1 c to Q6 c. In the secondthree-phase circuit 42, the FET Q1 c and the FET Q2 c are connected inseries to form a first series circuit; the FET Q3 c and the FET Q4 c areconnected in series to form a second series circuit; and the FET Q5 cand the FET Q6 c are connected in series to form a third series circuit.In the second three-phase circuit 42, the first series circuit isprovided on the isolation transformer 43 side; the third series circuitis provided on the high-voltage battery 50 side; the second seriescircuit is provided between the first series circuit and the thirdseries circuit; and the first, second, and third series circuits areconnected in parallel.

The second three-phase circuit 42 is connected to the isolationtransformer 43, the high-voltage battery 50, and the controller 80. Thecontroller 80 controls the FETs Q1 c to Q6 c of the second three-phasecircuit 42 between on and off. During the charging, the secondthree-phase circuit 42 converts the AC power supplied through theisolation transformer 43 into DC power, and outputs the DC power to thehigh-voltage battery 50. In contrast, during the AC power supply, thesecond three-phase circuit 42 converts DC power output from thehigh-voltage battery 50 into AC power, and outputs the AC power to theisolation transformer 43.

The isolation transformer 43 converts a voltage. The isolationtransformer 43 is provided between the first three-phase circuit 41 andthe second three-phase circuit 42, and transforms the voltage of thepower supplied through the first three-phase circuit 41 or the secondthree-phase circuit 42. The isolation transformer 43 includes three coilunits 43 a to 43 c. The coil unit 43 a includes primary winding L1 a,main secondary winding L2 a, and sub-secondary winding L3 a. The primarywinding L1 a is connected to one of the phases of the first three-phasecircuit 41. The primary winding L1 a is, for example, connected at oneend thereof to a line between the FET Q1 b and the FET Q2 b (firstphase) of the first three-phase circuit 41 through the coil L1 d, andconnected at the other end thereof to the other end of primary windingL1 b through a capacitor C1 d and to the other end of primary winding L1c through a capacitor C3 d.

The main secondary winding L2 a is electromagnetically coupled to theprimary winding L1 a, and is connected to one of the phases of thesecond three-phase circuit 42. The main secondary winding L2 a is, forexample, connected at one end thereof to a line between the FETs Q1 cand Q2 c (first phase) of the second three-phase circuit 42 through thecoil L4 d, and connected at the other end thereof to the other end ofmain secondary winding L2 b through a capacitor C4 d and to the otherend of main secondary winding L2 c through a capacitor C6 d.

The sub-secondary winding L3 a is electromagnetically coupled to theprimary winding L1 a and the main secondary winding L2 a, and isconnected to the sub-DC/DC converter 60. The sub-secondary winding L3 ais, for example, connected at one end thereof to a line between a diodeD1 and a diode D2 of a rectifier circuit 61 (to be described later), andconnected at the other end thereof to a line between a diode D3 and adiode D4 of the rectifier circuit 61.

In the same way, the coil unit 43 b includes the primary winding L1 b,the main secondary winding L2 b, and sub-secondary winding L3 b. Theprimary winding L1 b is connected to one of the phases of the firstthree-phase circuit 41. The primary winding L1 b is, for example,connected at one end thereof to a line between the FET Q3 b and the FETQ4 b (second phase) of the first three-phase circuit 41 through the coilL2 d, and connected at the other end thereof to the other end of primarywinding L1 a through the capacitor C1 d and to the other end of theprimary winding L1 c through a capacitor C2 d.

The main secondary winding L2 b is electromagnetically coupled to theprimary winding L1 b, and is connected to one of the phases of thesecond three-phase circuit 42. The main secondary winding L2 b is, forexample, connected at one end thereof to a line between the FETs Q3 cand Q4 c (second phase) of the second three-phase circuit 42 through thecoil L5 d, and connected at the other end thereof to the other end ofmain secondary winding L2 a through the capacitor C4 d and to the otherend of main secondary winding L2 c through a capacitor C5 d.

The sub-secondary winding L3 b is electromagnetically coupled to theprimary winding L1 b and the main secondary winding L2 b, and isconnected to the sub-DC/DC converter 60. The sub-secondary winding L3 bis, for example, connected at one end thereof to the line between thediode D3 and the diode D4 of the rectifier circuit 61, and connected atthe other end thereof to a line between a diode D5 and a diode D6 of therectifier circuit 61.

In the same way, the coil unit 43 c includes the primary winding L1 c,the main secondary winding L2 c, and sub-secondary winding L3 c. Theprimary winding L1 c is connected to one of the phases of the firstthree-phase circuit 41. The primary winding L1 c is, for example,connected at one end thereof to a line between the FET Q5 b and the FETQ6 b (third phase) of the first three-phase circuit 41 through the coilL3 d, and connected at the other end thereof to the other end of primarywinding L1 b through the capacitor C2 d and to the other end of theprimary winding L1 a through the capacitor C3 d.

The main secondary winding L2 c is electromagnetically coupled to theprimary winding L1 c, and is connected to one of the phases of thesecond three-phase circuit 42. The main secondary winding L2 c is, forexample, connected at one end thereof to a line between the FETs Q5 cand Q6 c (third phase) of the second three-phase circuit 42 through thecoil L6 d, and connected at the other end thereof to the other end ofmain secondary winding L2 b through the capacitor C5 d and to the otherend of main secondary winding L2 a through the capacitor C6 d.

The sub-secondary winding L3 c is electromagnetically coupled to theprimary winding L1 c and the main secondary winding L2 c, and isconnected to the sub-DC/DC converter 60. The sub-secondary winding L3 cis, for example, connected at one end thereof to the line between thediode D5 and the diode D6 (third phase) of the rectifier circuit 61, andconnected at the other end thereof to the line between the diode D1 andthe diode D2 of the rectifier circuit 61.

During the charging, the isolation transformer 43 increases the voltageof the AC power output from the first three-phase circuit 41, andoutputs the AC power increased in voltage to the second three-phasecircuit 42. In contrast, during the AC power supply, the isolationtransformer 43 reduces the voltage of the AC power output from thesecond three-phase circuit 42, and outputs the AC power reduced involtage to the first three-phase circuit 41.

The high-voltage battery 50 is a storage battery capable of storing theDC power. The high-voltage battery 50 includes a plurality of batterycells. Each of the battery cells is constituted by a chargeable anddischargeable secondary cell, for example, by a lithium-ion battery. Thebattery cells are arranged side by side, and are connected in seriesbetween adjacent battery cells. The high-voltage battery 50 has avoltage of, for example, roughly 200 V to 500 V. The high-voltagebattery 50 stores the DC power transformed by the main DC/DC converter40 during the charging, and supplies the DC power to the main DC/DCconverter 40 during the AC power supply. The high-voltage battery 50supplies the power to a high-voltage power supply system including, forexample, an inverter and a motor-generator.

The sub-DC/DC converter 60 converts the voltage of the DC power. Thesub-DC/DC converter 60 branches from the isolation transformer 43, andtransforms the voltage of the three-phase AC power supplied through thefirst three-phase circuit 41 or the second three-phase circuit 42. Thesub-DC/DC converter 60 includes the rectifier circuit 61 and thestep-down circuit 62. The rectifier circuit 61 rectifies the three-phaseAC power into DC power. The rectifier circuit 61 includes the diodes D1to D6. In the rectifier circuit 61, the diode D1 and the diode D2 areconnected in series along the forward direction to form a first seriescircuit; the diode D3 and the diode D4 are connected in series along theforward direction to form a second series circuit; and the diode D5 andthe diode D6 are connected in series along the forward direction to forma third series circuit. In the rectifier circuit 61, the first seriescircuit is provided on the isolation transformer 43 side; the thirdseries circuit is provided on the step-down circuit 62 side; the secondseries circuit is provided between the first series circuit and thethird series circuit; and the first, second, and third series circuitsare connected in parallel. As described above, the rectifier circuit 61is connected to the sub-secondary winding L3 a, L3 b, and L3 c of theisolation transformer 43. The rectifier circuit 61 rectifies thethree-phase AC power output from the sub-secondary winding L3 a, L3 b,and L3 c into the DC power. In this way, the rectifier circuit 61receives the three-phase AC power in which ripples have been canceledout, and therefore can perform the rectification processing on thestable power. The rectifier circuit 61 is connected to the step-downcircuit 62, and outputs the rectified DC power to the step-down circuit62. The rectifier circuit 61 may perform synchronous rectification usingswitching elements, instead of performing the rectification using thediodes D1 to D6. A smoothing capacitor C1 c is provided between therectifier circuit 61 and the step-down circuit 62.

The step-down circuit 62 is a step-down chopper circuit that reduces avoltage. The step-down circuit 62 includes a switching circuit 62 aincluding three switching elements that conduct or shut off currents, adiode unit 62 b including three diodes, and a coil unit 62 c includingthree coils that output currents through the diode unit 62 b in responseto operations of the switching circuit 62 a. The step-down circuit 62reduces the voltage of the DC power rectified by the rectifier circuit61, and outputs the DC power reduced in voltage to the low-voltagebattery 70. A smoothing capacitor C2 c is provided between the step-downcircuit 62 and the low-voltage battery 70.

The low-voltage battery 70 is a storage battery capable of storing theDC power. The low-voltage battery 70 is constituted by, for example, alithium-ion battery. The low-voltage battery 70 has a voltage of, forexample, roughly 12 V to 48 V. The low-voltage battery 70 stores the DCpower reduced in voltage by the sub-DC/DC converter 60. The low-voltagebattery 70 supplies power to a 12-volt power supply system having alower voltage than that of the high-voltage power supply system.

The controller 80 controls the conversion circuit 30, the main DC/DCconverter 40, and the sub-DC/DC converter 60. The controller 80 isconnected to, for example, the current sensor 21 a, the voltage sensor22 a, and the switching circuit 31 of the conversion circuit 30, andcontrols the switching circuit 31 of the conversion circuit 30 based ondetection results of the current sensor 21 a and the voltage sensor 22a. The controller 80 is connected to, for example, the current sensor 21b, the voltage sensor 22 b, and the first three-phase circuit 41 and thesecond three-phase circuit 42 of the main DC/DC converter 40, andperforms interleaved control of the first three-phase circuit 41 and thesecond three-phase circuit 42 based on detection results of the currentsensor 21 b and the voltage sensor 22 b. The term “interleaved control”refers to control of reducing the noise by canceling out the ripplesusing the three-phase alternating current in which the current andvoltage phases are offset from one another by 120 degrees. Thecontroller 80 is connected to the current sensor 21 c, the voltagesensor 22 c, and the step-down circuit 62 of the sub-DC/DC converter 60,and controls the step-down circuit 62 based on detection results of thecurrent sensor 21 c and the voltage sensor 22 c.

The following describes operation examples of the power conversiondevice 1. FIG. 2 is a circuit diagram illustrating a charging example ofthe power conversion device 1 according to the embodiment. Asillustrated, for example, in FIG. 2, during the charging, the conversioncircuit 30 of the power conversion device 1 converts the AC powersupplied from the AC power supply 2 into the DC power, and outputs theconverted DC power to the main DC/DC converter 40. The main DC/DCconverter 40 increases the voltage of the DC power output from theconversion circuit 30, and outputs the DC power increased in voltage tothe high-voltage battery 50. During the charging, the main DC/DCconverter 40 outputs the three-phase AC power to the sub-DC/DC converter60 branching from the isolation transformer 43. The sub-DC/DC converter60 converts the three-phase AC power output from the main DC/DCconverter 40 into the DC power, and reduces the voltage of the convertedDC power. The sub-DC/DC converter 60 outputs the DC power reduced involtage to the low-voltage battery 70.

FIG. 3 is a circuit diagram illustrating an AC power supply example ofthe power conversion device 1 according to the embodiment. Asillustrated, for example, in FIG. 3, during the AC power supply, themain DC/DC converter 40 of the power conversion device 1 reduces thevoltage of the DC power supplied from the high-voltage battery 50, andoutputs the DC power reduced in voltage to the conversion circuit 30.The conversion circuit 30 converts the DC power output from the mainDC/DC converter 40 into the AC power, and outputs the converted AC powerto the load unit 3 through the filter 10. During the AC power supply,the main DC/DC converter 40 outputs the three-phase AC power to thesub-DC/DC converter 60 branching from the isolation transformer 43. Thesub-DC/DC converter 60 rectifies the three-phase AC power output fromthe main DC/DC converter 40 into the DC power, and reduces the voltageof the rectified DC power. The sub-DC/DC converter 60 outputs the DCpower reduced in voltage to the low-voltage battery 70.

The following describes an output power limitation example during the ACpower supply. FIG. 4 is a flowchart illustrating the power limitationexample during the AC power supply according to the embodiment. Asillustrated in FIG. 4, the controller 80 of the power conversion device1 acquires an output current and an output voltage of the sub-DC/DCconverter 60 from the current sensor 21 c and the voltage sensor 22 c(Step S1). The controller 80 then determines whether the sub-DC/DCconverter 60 is in operation (Step S2). When the sub-DC/DC converter 60is in operation (Yes at Step S2), the controller 80 obtains output powerof the sub-DC/DC converter 60 (Step S3). The controller 80 obtains theoutput power of the sub-DC/DC converter 60, for example, based on theoutput current and the output voltage of the sub-DC/DC converter 60acquired at Step S1 described above.

The controller 80 then obtains a power limitation value for theconversion circuit 30 based on a predetermined maximum value of outputpower of the conversion circuit (AC inverter) 30 and the value of theoutput power of the sub-DC/DC converter 60 obtained at Step S3 describedabove (Step S4). The controller 80 obtains the power limitation valuefor the conversion circuit 30, for example, by subtracting the value ofthe output power of the sub-DC/DC converter 60 obtained at Step S3described above from the maximum value of the output power of theconversion circuit 30. The controller 80 changes the power limitationvalue for the conversion circuit 30 to the power limitation valueobtained at Step S4 described above (Step S5). During the AC powersupply, the controller 80 controls the conversion circuit 30 based onthe changed power limitation value to limit the AC power output from theconversion circuit 30 to power having the power limitation value. If, atStep S2 described above, the sub-DC/DC converter 60 is not in operation(No at Step S2), the controller 80 changes the power limitation valuefor the conversion circuit (AC inverter) 30 to the maximum value of theoutput power of the conversion circuit (AC inverter) 30 (Step S6).

As described above, the power conversion device 1 is mounted on thevehicle, and is provided with the main DC/DC converter 40 and thesub-DC/DC converter 60. The main DC/DC converter 40 includes the firstthree-phase circuit 41 capable of receiving and outputting thethree-phase alternating current, the second three-phase circuit 42capable of receiving and outputting the three-phase alternating current,and the isolation transformer 43. The sub-DC/DC converter 60 branchesfrom the isolation transformer 43, and transforms the voltage of thepower supplied through the first three-phase circuit 41 or the secondthree-phase circuit 42. The isolation transformer 43 is provided betweenthe first three-phase circuit 41 and the second three-phase circuit 42,and transforms the voltage of the power supplied through the firstthree-phase circuit 41 or the second three-phase circuit 42. Theisolation transformer 43 includes the three coil units 43 a to 43 c. Thecoil unit 43 a (43 b, 43 c) includes the primary winding L1 a (Lib, L1c), the main secondary winding L2 a (L2 b, L2 c), and the sub-secondarywinding L3 a (L3 b, L3 c). The primary winding L1 a (Lib, L1 c) isconnected to one of the phases of the first three-phase circuit 41. Themain secondary winding L2 a (L2 b, L2 c) is electromagnetically coupledto the primary winding L1 a (Lib, L1 c), and is connected to one of thephases of the second three-phase circuit 42. The sub-secondary windingL3 a (L3 b, L3 c) is electromagnetically coupled to the primary windingL1 a (Lib, L1 c) or the main secondary winding L2 a (L2 b, L2 c), and isconnected to the sub-DC/DC converter 60. The coil units 43 a to 43 c areprovided in the three phases, at least one for each phase.

With the above-described configuration, the power conversion device 1can perform the interleaved control of the first three-phase circuit 41and the second three-phase circuit 42 of the main DC/DC converter 40 soas to cancel out the ripples of the three-phase alternating current toreduce the noise. Accordingly, the power conversion device 1 can reducethe ripples supplied to the sub-DC/DC converter 60, and thus can supplythe stable power from the sub-DC/DC converter 60 to the low-voltagebattery 70. In the power conversion device 1, the isolation transformer43 can be used as the transformer for the in-vehicle charger, the DC/DCconverters, and the AC inverter. Accordingly, the power conversiondevice 1 can restrain an increase in size of the device, and can reducethe manufacturing cost. The power conversion device 1 is provided withthe sub-DC/DC converter 60, and thereby can reduce a drop in amount ofcharge of the low-voltage battery 70 during the charging and during theAC power supply. In the power conversion device 1, since the sub-DC/DCconverter 60 branches from the isolation transformer 43 by way of thesub-secondary winding L3 a (L3 b, L3 c), a switching relay or the likeis not required, and the number of parts can be reduced. As a result,the power conversion device 1 can appropriately supply a plurality ofkinds of power having different voltages.

The power conversion device 1 described above is provided with theconversion circuit 30 and the high-voltage battery 50. The conversioncircuit 30 outputs the DC power converted from the AC power suppliedfrom the AC power supply 2 to the main DC/DC converter 40. Thehigh-voltage battery 50 stores the DC power transformed by the mainDC/DC converter 40. This configuration allows the power conversiondevice 1 to charge the high-voltage battery 50 using the main DC/DCconverter 40, and to charge the low-voltage battery 70 using thesub-DC/DC converter 60.

In the power conversion device 1 described above, during the AC powersupply, the high-voltage battery 50 supplies the DC power to the mainDC/DC converter 40. The conversion circuit 30 outputs the AC powerconverted from the DC power transformed by the main DC/DC converter 40to the load unit 3. This configuration allows the power conversiondevice 1 to supply the AC power to the load unit 3 using the main DC/DCconverter 40 and the conversion circuit 30, and to charge thelow-voltage battery 70 using the sub-DC/DC converter 60.

The power conversion device 1 described above is provided with thecontroller 80 that controls the conversion circuit 30 and the sub-DC/DCconverter 60. The controller 80 limits the output power output from theconversion circuit 30 to the load unit 3 based on the maximum value ofthe output power output from the conversion circuit 30 to the load unit3 and the output power actually output from the sub-DC/DC converter 60.This configuration allows the power conversion device 1 to perform theAC supply to the load unit 3 according to the charging power to thelow-voltage battery 70. For example, the power conversion device 1relatively reduces the power of the AC supply to the load unit 3 whenthe charging power to the low-voltage battery 70 is relatively high, andrelatively increases the power of the AC supply to the load unit 3 whenthe charging power to the low-voltage battery 70 is relatively low.Accordingly, the power conversion device 1 can appropriately supply thepower to the load unit 3 while ensuring the charging power to thelow-voltage battery 70.

Modification

The following describes a modification of the embodiment. FIG. 5 is aflowchart illustrating a power limitation example during the AC powersupply according to the modification of the embodiment. The exampleillustrated in FIG. 5 differs from the embodiment in that the powerlimitation value is obtained based on the maximum value of the outputpower of the sub-DC/DC converter 60. As illustrated in FIG. 5, thecontroller 80 of the power conversion device 1 determines whether thesub-DC/DC converter 60 is in operation (Step T1). When the sub-DC/DCconverter 60 is in operation (Yes at Step T1), the controller 80 obtainsthe power limitation value based on the predetermined maximum value ofthe output power of the conversion circuit (AC inverter) 30 and thepredetermined maximum value of the output power of the sub-DC/DCconverter 60 (Step T2). The controller 80 obtains the power limitationvalue for the conversion circuit 30, for example, by subtracting themaximum value of the output power of the sub-DC/DC converter 60 from themaximum value of the output power of the conversion circuit 30. Thecontroller 80 changes the power limitation value for the conversioncircuit (AC inverter) 30 to the power limitation value obtained at StepT2 described above (Step T3). During the AC power supply, the controller80 controls the conversion circuit 30 based on the changed powerlimitation value to limit the AC power output from the conversioncircuit 30 to power having the power limitation value. If, at Step T1described above, the sub-DC/DC converter 60 is not in operation (No atStep T1), the controller 80 changes the power limitation value for theconversion circuit (AC inverter) 30 to the maximum value of the outputpower of the conversion circuit (AC inverter) 30 (Step T4).

As described above, in the power conversion device 1 described above,the controller 80 limits the output power output from the conversioncircuit 30 to the load unit 3 based on the maximum value of the outputpower that is the power output from the conversion circuit 30 to theload unit 3 and the maximum value of the output power of the sub-DC/DCconverter 60. This configuration allows the power conversion device 1 toperform the AC power supply to the load unit 3 while ensuring themaximum value of the charging power to the low-voltage battery 70.Accordingly, the power conversion device 1 can charge the low-voltagebattery 70 while stably performing the AC power supply to the load unit3 even when the charging power to the low-voltage battery 70 has reachedthe maximum during the AC power supply to the load unit 3.

FIG. 6 is a circuit diagram illustrating an isolation transformer 43Aaccording to the modification of the embodiment. The isolationtransformer 43A differs from the isolation transformer 43 according tothe embodiment in the connection of the primary winding L1 a to L1 c tothe resonant circuit. As illustrated, for example, in FIG. 6, in theisolation transformer 43A, the primary winding L1 a is connected at oneend thereof to the line between the FET Q1 b and the FET Q2 b of thefirst three-phase circuit 41 through the resonance coil L1 d, andconnected at the other end thereof to a ground through the resonancecapacitor C1 d; the primary winding L1 b is connected at one end thereofto the line between the FET Q3 b and the FET Q4 b of the firstthree-phase circuit 41 through the resonance coil L2 d, and connected atthe other end thereof to the ground through the resonance capacitor C2d; and the primary winding L1 c is connected at one end thereof to theline between the FET Q5 b and the FET Q6 b of the first three-phasecircuit 41 through the resonance coil L3 d, and connected at the otherend thereof to the ground through the resonance capacitor C3 d. In thisway, the primary winding L1 a to L1 c of the isolation transformer 43Ais connected to the resonant circuit.

FIG. 7 is a circuit diagram illustrating an isolation transformer 43Baccording to the modification of the embodiment. The isolationtransformer 43B differs from the isolation transformer 43 according tothe embodiment in the connection of the primary winding L1 a to L1 c tothe resonant circuit. As illustrated, for example, in FIG. 7, in theisolation transformer 43B, the primary winding L1 a is connected at oneend thereof to the line between the FET Q1 b and the FET Q2 b of thefirst three-phase circuit 41 through the resonance coil L1 d, andconnected at the other end thereof to the other end of the primarywinding L1 b and the other end of the primary winding L1 c through theresonance capacitor C1 d; the primary winding L1 b is connected at oneend thereof to the line between the FET Q3 b and the FET Q4 b of thefirst three-phase circuit 41 through the resonance coil L2 d, andconnected at the other end thereof to the other end of the primarywinding L1 a and the other end of the primary winding L1 c through theresonance capacitor C2 d; and the primary winding L1 c is connected atone end thereof to the line between the FET Q5 b and the FET Q6 b of thefirst three-phase circuit 41 through the resonance coil L3 d, andconnected at the other end thereof to the other end of the primarywinding L1 a and the other end of the primary winding L1 b through theresonance capacitor C3 d. In this way, the primary winding L1 a to L1 cof the isolation transformer 43B is connected to the resonant circuit.

In the description above, the example has been described in which theAC/DC circuit and the inverter circuit of the power conversion device 1are constituted by the same conversion circuit 30. The power conversiondevice 1 is, however, not limited to this example. The AC/DC circuit andthe inverter circuit of the power conversion device 1 may be constitutedby different circuits from each other.

Although the example has been described in which the power conversiondevice 1 is capable of performing both the charging and the AC powersupply, the power conversion device 1 is not limited to this example.The power conversion device 1 may perform, for example, only either oneof the charging and the AC power supply.

Although the example has been described in which the power conversiondevice 1 charges both the high-voltage battery 50 and the low-voltagebattery 70 during the charging, the power conversion device 1 is notlimited to this example. For example, during the charging, the powerconversion device 1 may charge the high-voltage battery 50 while notcharging the low-voltage battery 70.

Although the example has been described in which the power conversiondevice 1 supplies the power to the load unit 3 and charges thelow-voltage battery 70 during the AC power supply, the power conversiondevice 1 is not limited to this example. For example, during the ACpower supply, the power conversion device 1 may supply the power to theload unit 3 while not charging the low-voltage battery 70.

The power conversion device 1 may use the power supplied from thehigh-voltage battery 50 to charge the low-voltage battery 70 during aperiod other than the charging period and the AC power supply period.

Although the example has been described in which the power conversiondevice 1 is provided with the conversion circuit 30 and the high-voltagebattery 50, the power conversion device 1 is not limited to thisexample, and need not be provided with the conversion circuit 30 and thehigh-voltage battery 50.

Although the example has been described in which the power conversiondevice 1 limits the output power output from the conversion circuit 30to the load unit 3, the power conversion device 1 is not limited to thisexample, and need not limit the output power output from the conversioncircuit 30 to the load unit 3.

Although the example has been described in which the sub-DC/DC converter60 is provided with the step-down circuit 62, the sub-DC/DC converter 60is not limited to this example, and may be provided with a step-upcircuit or a step-up/down circuit instead of the step-down circuit 62.

The power conversion device according to the embodiment is provided withthe sub-DC/DC converter branching from the isolation transformer of themain DC/DC converter capable of receiving and outputting the three-phasealternating current, and therefore can reduce the ripples of the powersupplied to the sub-DC/DC converter and can appropriately supply aplurality of kinds of power having different voltages.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

What is claimed is:
 1. A power conversion device mounted on a vehicleand comprising: a main DC/DC converter including a first three-phasecircuit capable of receiving and outputting a three-phase alternatingcurrent, a second three-phase circuit capable of receiving andoutputting a three-phase alternating current, and an isolationtransformer provided between the first three-phase circuit and thesecond three-phase circuit, and configured to transform a voltage ofpower supplied through the first three-phase circuit or the secondthree-phase circuit; and a sub-DC/DC converter branching from theisolation transformer, and configured to transform the voltage of thepower supplied through the first three-phase circuit or the secondthree-phase circuit, wherein the isolation transformer includes threecoil units each having a primary winding connected to one of phases ofthe first three-phase circuit, a main secondary windingelectromagnetically coupled to the primary winding, and connected to oneof phases of the second three-phase circuit, and a sub secondary windingelectromagnetically coupled to the primary winding or the main secondarywinding, and connected to the sub-DC/DC converter, and the coil unitsare provided in the three phases, at least one for each phase.
 2. Thepower conversion device according to claim 1, further comprising: anAC/DC circuit configured to output, to the main DC/DC converter, adirect current power converted from an alternating current powersupplied from an alternating current power supply; and a power storageunit configured to store the direct current power transformed by themain DC/DC converter.
 3. The power conversion device according to claim1, further comprising: a power storage unit configured to store a directcurrent power and supply the direct current power to the main DC/DCconverter; and an inverter circuit configured to output, to a load unit,an alternating current power converted from the direct current powertransformed by the main DC/DC converter.
 4. The power conversion deviceaccording to claim 2, further comprising: a power storage unitconfigured to store a direct current power and supply the direct currentpower to the main DC/DC converter; and an inverter circuit configured tooutput, to a load unit, an alternating current power converted from thedirect current power transformed by the main DC/DC converter.
 5. Thepower conversion device according to claim 3, further comprising: acontroller configured to control the inverter circuit and the sub-DC/DCconverter, wherein the controller is configured to limit output poweroutput from the inverter circuit to the load unit based on a maximumvalue of the output power and an output value of the sub-DC/DCconverter.